1. Field of the Disclosure
The present disclosure relates to a magnetic detection device that detects, with a magnetic sensor such as a GMR element, a magnetic field component in a direction perpendicular to a sensitivity axis thereof.
2. Description of the Related Art
In each of magnetic detection devices disclosed in Japanese Unexamined Patent Application Publication No. 2009-276159 and International Publication No. 2011/068146, a bridge circuit is composed of magnetoresistance effect elements a sensitivity axis of each of which is directed in the horizontal direction, and each magnetoresistance effect element is provided with magnetic bodies that are each formed from a soft magnetic material extending in the vertical direction and opposed to each other. A magnetic field component in the vertical direction is guided by the magnetic bodies, and a component, in the horizontal direction, of a leakage flux from a lower end portion of each magnetic body is detected with the magnetoresistance effect element. Accordingly, it is possible to detect the intensity of a magnetic field in the vertical direction.
In the magnetic detection device, it is required that a detection output based on a component, in the horizontal direction, of an external magnetic field is not superimposed on an original detection output. Thus, the bridge circuit is configured such that even when the resistance values of the respective magnetoresistance effect elements are changed by a magnetic field component in the horizontal direction, the changes are cancelled out.
In the magnetic detection device, each magnetic body for guiding a magnetic field in the vertical direction is formed from a soft magnetic material having a high magnetic permeability. However, if the magnetic permeability of each magnetic body is high, the sensitivity is varied with respect to a magnetic field component in the horizontal direction that originally should not be detected.
That is, in such a magnetic detection device, when a magnetic field component in the horizontal direction is applied to a plurality of magnetoresistance effect elements at the same intensity, even if the resistance values of the magnetoresistance effect elements are changed, the changes of the resistance values are cancelled out so as not to appear as a detection output. However, if the magnetic permeability of each magnetic body is high, since a magnetic field component in the horizontal direction is drawn to the magnetic bodies, the intensity of the magnetic field in the horizontal direction applied to each magnetoresistance effect element is likely to be varied. If the variation is increased, it is made impossible to cancel out the changes of the resistance values in the bridge circuit, and a detection output corresponding to the intensity of a magnetic field in the horizontal direction that originally should not be detected appears as detection noise.
Therefore, a counter-measure is conceivable that the soft magnetic characteristics of each magnetic body are deteriorated to decrease the magnetic permeability thereof, whereby a magnetic field component in the horizontal direction is less likely to be drawn to the magnetic body. However, when the soft magnetic characteristics of the magnetic body are deteriorated, a coercive force thereof is increased. Thus, when a relatively great external magnetic field is applied, magnetization is likely to remain within the magnetic body. As a result, in detecting a magnetic field component in the vertical direction, an offset component is superimposed on a detection output, and the sensitivity is varied.
The present invention solves the above problems of the related art and provides a magnetic detection device having a structure in which a magnetic field component directed in a sensitivity axis of a magnetic sensor is less likely to be superimposed as noise and the magnetic detection device is less subject to influence of a strong magnetic field externally applied thereto.